Magnetic resonance imaging (MRI) is a medical imaging tool that provides cross-sectional images or “slices” of a human body. Major advantages of the MRI compared to other medical imaging techniques are high contrast sensitivity to soft tissue differences, high spatial resolution, ease of 2-dimensional (2D) and 3-dimensional (3D) imaging and patient safety due to use of non-ionizing radiation. Therefore, the MRI is presently the primary choice for cross-sectional imaging of the human body over many CT/X-ray and other tomography imaging techniques. Recently, the MRI has experienced substantial improvements in image quality due to introduction of novel MRI acquisition methods and equipment design. Today, the MRI is the preferred diagnostic tool for imaging studies such as neuro-radiological exams and applications continuously grow in areas thought not possible a few years ago such as 3D cardiac imaging.
During the MRI data acquisition process the patient is placed in a strong magnetic field of approximately 1 to 3 Tesla and a radio wave is radiated into the patient's body for a short duration. As a result the patient's body first absorbs the radio wave and then emits radio-frequency signals containing information about the spatial distribution of nuclear magnetization at a pre-selected cross section of the patient's body. This information is then used to produce the cross-sectional image employing Fourier transformation techniques.
One major disadvantage of the MRI is the relatively long data-acquisition time in order to produce high quality, diagnostically interpretable images. Unfortunately, the duration of the data acquisition is long enough—of the order of a few seconds—for organ motion such as cardiac motion, respiration, blood flow, peristalsis or restlessness to cause artifacts such as blurring and replication—commonly termed as ghosting—in the reconstructed image. As is evident, such artifacts substantially impede diagnosis or even lead to erroneous diagnosis. Numerous techniques for removing these artifacts have been disclosed in the following references which are hereby incorporated by reference:
Atalar, E., Onural, L., “A Respiratory Motion Artifact Reduction Method in Magnetic Resonance Imaging of the Chest”, IEEE Transactions on Medical Imaging, Vol. 10, pp. 11-24, March 1991;
Axel, L., Summers, R. M., Kressel, H. Y., and Charles, C., “Respiratory effects in two-dimensional Fourier transform MR imaging”, Radiology 160, pp. 795-801, 1986;
Bails, D. R., Glendale, D. J., Bydder, G. M., Collins, A. G., and Firmin, D. N., “Respiratory Ordered Phase Encoding (ROPE): A Method for Reducing Respiratory Motion Artifacts in MR Imaging”, J. Comput. Assist. Tomogr., 9, 835, 1985;
Haacke, E. M., and Patrik, J. L., “Reducing Motion Artifacts in Two-dimensional Fourier Transform Imaging”, Magnetic Resonance Imaging, 4, pp. 359-376, 1986;
Lauzon, M. L., and Rutt, B. K., “Generalized K-Space Analysis and Correction of Motion Effects in MR Imaging”, Magnetic Resonance in Medicine, 30, pp. 438-446, 1993;
McConnell, M. V., Khasgiwala, V. C., Savord, B. J., Chen, M. H., Chuang, M. L., Edelman, R. R., and Manning, W. J., “Prospective Adaptive Navigator Correction for Breath-Hold MR Coronary Angiography”, Magnetic Resonance in Medicine, 37, pp. 148-152, 1997; and,
Wood, M. L., and Henkelman, R. M., “Suppression of respiratory motion artifacts in magnetic resonance imaging”, Med. Phys. J., Vol. 13, 794, 1986.
Although the correction methods disclosed in the above cited references are effective under certain conditions, none of these methods completely eliminates the motion artifacts from the produced cross-sectional images. In particular, these methods do not substantially reduce the motion artifacts in case of more general motion effects such as combined cardiac and respiratory motion effects.